Pneumatic devices commonly referred to as air springs, have been used with motor vehicles for a number of years to provide cushioning between movable parts of the vehicle suspension, primarily to absorb shock loads impressed on the vehicle axles by the wheels striking an object in the road or falling into a depression. These air springs usually consist of a flexible elastomeric sleeve or bellows containing a supply of compressed air or other fluid which is compressed or expanded as the vehicle experiences the road shock. The fluid is compressed and expanded within the spring sleeve since the sleeve is of a flexible material. The ends of the sleeve usually are sealingly connected to a top member or a lower piston member and have one or more rolled ends which permit the attachment or end members to move axially with respect to each other between a jounce or collapse position and a rebound or extended position without damaging the flexible sleeve.
It is desirable for many applications that a damping mechanism or device be used in combination with such air springs to provide damping for controlling the movement of the air spring. One type of vehicle damping or shock absorbing is achieved through a separate shock absorbing strut such as a McPherson strut, which uses a cylinder and a piston rod reciprocally mounted in the cylinder in combination with the air spring. The bottom of the cylinder is connected by an attachment bracket to one part of the vehicle and the piston rod or upper portion of the suspension system is attached to a separate spaced part of the vehicle for absorbing the road shocks exerted on the vehicle axles. In such suspension systems which use a strut-type fluid shock absorber it is desirable that the strut shaft or piston rod be isolated, usually in an elastomer, form the vehicle chassis and when used with an air spring to isolate it from the air canister which preferably is isolated in an elastomer from the vehicle chassis.
Some examples of vehicle suspension systems using strut-type fluid shock absorbers and isolator mounts without an air spring are shown in U.S. Pat. Nos. 4,248,454, 4,319,768, 4,478,396, 4,434,977, 4,256,292, 4,274,655, 4,289,193 and 4,531,759.
Other examples of prior art suspension systems which use a strut-type fluid shock absorber in combination with an air spring and an isolator mount for the shock absorber are shown in the following patents.
U.S. Pat. No. 3,046,000 shows a suspension system in which the top end of the piston rod is encapsulated in a rubber element bonded within a cylindrical cup which is attached to a separate spring assembly, cup the lower end of which has the bellows sleeve of a flexible diaphragm connected thereto.
U.S. Pat. No. 3,373,919 shows a vehicle strut having a flexible sleeve extending between a dust shield and a piston cylinder for containing a pressurized fluid so that the air spring unit will be maintained between predetermined pressure levels.
U.S. Pat. No. 4,555,096 discloses a suspension system in which the top of the piston rod is attached to the vehicle chassis through an elastomeric isolator in combination with a flexible sleeve which forms an air spring in combination with a rigid upper cup shaped member which compresses the isolator or rubber mount between the top wall of the canister and the mounting bracket for the piston rod. One of the main problems with suspension units such as shown in this patent is the ability to provide satisfactory air seals for the air sleeve at its junction with the piston rod and/or cylinder and isolator mount.
U.S. Pat. No. 4,592,540 shows another suspension unit having an air sleeve extending between the bottom of a cylindrical upper member or housing which forms the pressurized fluid chamber, and a separate isolator mount which connects the piston rod to the vehicle chassis. Again, such a suspension system requires multiple parts which must be manufactured and assembled thereby increasing the cost of the unit, and it requires complicated air seals for the pressure chamber of the air spring.
Japanese Pat. No. 60-241538 shows another combination air spring and strut-type fluid shock absorber in which the piston rod is connected through an isolator mount to the vehicle chassis. United Kingdom Pat. No. 846,244 shows still another type of suspension unit combining an air spring with a fluid shock absorber.
Although many of these prior art suspension systems perform satisfactorily for their intended function, these as well as other known suspension units, require that the upper isolator mount for the air spring and strut-type fluid shock absorber requires a number of separate components which increases the cost of the final unit and the assembling thereof. Also, the cost of mounting such a multiple component unit on a vehicle in an assembly line is increased, and since many of these suspension units require complicated air seals they periodically must be replaced and repaired after a period of use on a vehicle.
Therefore, the need exists for a suspension system using a strut-type fluid shock absorber in combination with an air spring and an isolator mount for mounting the system onto a vehicle chassis, in which the suspension system has a reduced number of parts without the loss of efficiency and desirable results achieved by the suspension system.